I don't buy any commercial dog food as I found it bad for my dog.
My dog had skin problems and developed dental problems also, despite me only feeding dry dog food, dental dog chews and brushing her teeth. I did research and was desperate for ideas to help my dog.............then I decided to change to a natural diet. My dog was cured of her skin allergies in less than 3 months, and a few more weeks her teeth are perfect and I never brush them now!
So now I feed my dog raw meet and bones only. I don't add any vitamins, vegetables or anything. She eats all meats, and also the organs - she loves hearts and liver.
I worked in a well know pet store chain in the UK for many years and I can tell you that what they put in most dry dog foods is nothing more than hight temperature baked corn, cereals and waste meat bi products from the food industry that are unfit for human consumption. The cooking process destroys any goodness in the food, and so they have to add chemical or artificial vitamins minerals and other stuff. Also they add lots of salt, sugar and preservatives, which are not good for the animals health.